Recently, liquid crystal displays have widely been applied as display devices of personal computers, television sets, word processing machines, video eras, etc. on the other hand, further higher performance such as downsizing, energy saving, cost reduction, etc., has been required of such apparatuses. In order to meet these requests, a reflection type liquid crystal device that is able to display by reflecting surrounding light incident from the peripheries without using any backlight (there is a type in which a backlight is used in a dark place) has been progressively developed.
In such a reflection type liquid crystal display, as any backlight is not used, it is important how much the display surface can be made bright by further efficiently utilizing the surrounding light. Therefore, a role achieved by a reflection plate, which is incorporated in the reflection type liquid crystal display, is remarkably important, wherein it is desired that a reflection plate having optimal reflection characteristics, which efficiently utilizes the surrounding light coming from any angle, is developed.
Basically, a reflection plate 1 used for a reflection type liquid crystal display device is, as shown in FIG. 1, disposed at the rear side of a liquid crystal panel 2, and regularly reflects the incident surrounding light. However, in such a simple reflection plate 1, a problem occurs in that the reflection light from the surface of the liquid crystal panel 2 is brought in. That is, when surrounding light such as sunlight, indoor illumination light, etc., is made incident into a liquid crystal device, a part of the surrounding light is reflected from the surface of the liquid crystal panel 2 as shown in FIG. 1, and the remaining surrounding light penetrates the liquid crystal panel 2 and is reflected by the reflection plate 1, wherein if the reflection direction of the reflection light on the surface of the liquid crystal panel 2 is identical to that of the reflection light by the reflection plate 1, the light source is brought in on image appearing on the liquid crystal device, and it becomes difficult to recognize the image. That is, visible recognition is worsened.
In order to solve these and other problems, such a type has been proposed, in which a pattern consisting of a number of recesses and projections 3 is arrayed on the surface of the reflection plate 1 as shown in FIG. 2(a) and incident light is scattered and reflected by the respective recesses and projections 3 as shown in FIG. 2(b). If it is devised that light incident into the reflection plate 1 is scattered by the recesses and projections 3, it is possible to observe the screen from a direction where a viewer is not disturbed by any light that is regularly reflected by the liquid crystal panel 2, wherein visible recognition performance of the liquid crystal display can be improved. In addition, where the recesses and projections 3 are designed so as to have a recess and projection profile by which an inclination angle of the recesses and projections 3 (an inclination angle of the tangential plane of the recesses and projections) do not exceed α as shown in FIG. 3, it is possible to control the emission direction of the reflection light so that the emission direction is not widened more than 2β, wherein, by adjusting the angle α, it becomes possible to make the screen bright by narrowing the angle of the field of vision or to widen the angle of the field of vision by sacrificing the brightness thereof.
However, since the recess and projection profile is the same at any position of the reflection plate 1 as shown in FIG. 2., light is reflected in useless directions, and utilization efficiency of the light is worsened. FIG. 4 is a view describing the above-described shortcoming. In the drawing, it is assumed that recesses and projections 3 are formed in the reflection plate 1 so that spread in the reflection direction becomes 2β. FIG. 4 shows light that is reflected at both left and right ends of the reflection plate 1 where the incident light is made incident vertically into the reflection plate 1. Area I is an area where no light reflected from the reflection plate 1 reaches (that is, an area where no screen is observed). Area II is an area where light reflected from only a part of the reflection plate 1 reaches (that is, an area where only a part of the screen is observed). Area IV is an area where, although light reflected from entire of the reflection plate can reach, no screen is observed since the light is hindered by entire of the reflection light of a liquid crystal panel 2. Area III is an area where entire of the screen of the liquid crystal panel 2 can be observed (That is, an effective field of vision area.).
Although, in FIG. 4, an area where the screen can be observed is expressed from a direction perpendicular to the reflection plate 1, FIG. 5 shows an area where a screen which is observed from the front side of the reflection plate 1 is observed. Herein, a case where light is made incident into one corner of the reflection plate 1 is taken into consideration. As shown in FIG. 6, since the light reflected by the reflection plate 1 spreads in a range of angle α, an area where the reflection light reaches enters the interior of a circle whose radius is h tanα centering around the perpendicular line erected at the corner of the reflection plate 1 where it is assumed that the distance to the point of view is h (that is, the distance to a position of an eye which observes a screen, for example, a distance of clear vision). Therefore, where consideration is taken with respect to a plane parallel to the reflection plate 1 including the point of view, only a part of light reflected by entire of the reflection plate reaches in Area II in FIG. 5, thereby allowing a part of the screen to be observed, and in Area I outside Area II, no light reflected by the reflection plate 1 reaches, thereby allowing no screen to be observed. In Area IV, although light reflected from entire of the reflection plate reaches, the light is hindered by regular reflection light brought about by the liquid crystal panel 2, thereby allowing no screen to be observed. Therefore, an area where light reflected from entire of the reflection plate reaches to allow the entire screen to be observed is only the area (Area III) indicated by diagonal lines in FIG. 5.
Thus, an area where the entire screen of the liquid crystal panel can be observed is only Area III in FIG. 4 or FIG. 5. In Areas II and IV, even if light reflected from the reflection plate 1 reaches, it is impossible to observe the entire screen, or since the reflected light is hindered by regular reflection light from a light source, it is impossible to observe images, wherein all light reflected toward Areas II and Iv because useless, and the screen observed from the direction of Area III resultantly becomes dark.
Also, as shown in FIG. 4 or FIG. 5, it is understood that an amount of light corresponding to the useless portions of light reflected toward useless directions by the reflection plate 1 is remarkable.